Although the hippocampus makes use of the neocortex (if a particular brain has one) as its scratch pad, its memory is not inherently hierarchical. Animals without a neocortex can accordingly remember things using their hippocampus, but their recollections will not be hierarchical.

The capacity of the hippocampus is limited, so it's memory is short-term. It will transfer a particular sequence of patterns from its short-term memory to the long-term hierarchical memory of the neocortex by playing this memory sequence to the neocortex over and over again. We need, therefore a hippocampus in order to learn new memories and skills (although strictly motor skills appear to use a different mechanism). Someone with damage to both copies of her hippocampus will retain her existing memories but will not be able to form new ones.

University of Southern California neuroscientist Theodore Berger and his colleagues modeled the hippocampus of a rat and have successfully experimented with implanting an artificial one. In a study reported in 2011, the USC scientists blocked particular learned behaviors in rats with drugs. Using an artificial hippocampus, the rats were able to quickly relearn the behavior. "Flip the switch on, and the rats remember. Flip it off and the rats forget." Berger wrote, referring to his ability to control the neural implants remotely. In another experiment the scientists allowed their artificial hippocampus to work alongside the rats' natural one. The result was that the ability of the rats to learn new behaviors strengthened. "These integrated experimental modeling studies show for the first time," Berger explained, "that...a neural prosthesis capable of real-time identification and manipulation of the encoding process can restore and even enhance cognitive mnemonic processes."7 The hippocampus is one of the first regions damaged by Alzheimer's, so one goal of this research is to develop a neural implant for humans that will mitigate this first phase of damage from the disease.